Devices to control the oscillatory inflation and deflation of bladders for massaging and the like purposes as well as for medical treatment are well known in the art. See Summerville U.S. Pat. No. 2,684,672; Proctor U.S. Pat. No. 5,109,832 and Petajan et al U.S. Pat. No. 5,197,461 and the references cited therein.
The object of the present invention is to produce oscillation (inflation and deflation) of a bladder for massaging and medical purposes using the principle of a venting relief valve which has a high hysteresis.